DALLAS — Jeff Van Gundy felt he didn’t need to talk to Chris Dudley about the cold, hard fact that he’s out of the rotation for the time being. But Van Gundy felt differently about advising John Wallace, the struggling forward who on some nights won’t get in the game with the return of Patrick Ewing and Larry Johnson.

Van Gundy said the Wallace situation is “game by game.”

“We have eight, and then it’s how the game goes,” Van Gundy said. Both Wallace and Dudley didn’t play in last night’s 100-93 win over the Mavericks. Wallace is not part of the elite eight.

“I consider John a little different,” Van Gundy said about his briefing. “He’s a younger player and hasn’t been around as long. To me, it’s a different situation. It’s just important they handle it well and stay ready.”

Wallace, signed in the summer to give the Knicks another low-post scorer, is shooting just 39 percent and hasn’t excelled on the defensive end — which is not his strength anyway.

“He’s a better offensive player than he’s playing so far in preseason and regular season,” Van Gundy said. “It’s a frustation for him I know. He’s gotten good shots but 39 percent is uncharacteristic.”

Van Gundy is considering using Dudley for his offensive rebounding but Dudley has played one minute in the past four games since Ewing’s return while center Andrew Lang has posted four straight DNPs.

“If I called on them, I don’t know how they’d play but I know they’d be ready,” Van Gundy said.

Van Gundy is hardly thrilled the Knicks are playing on Christmas Day. Worse, they’re on the road, facing Indiana for NBC programming in a battle of last season’s Eastern Conference finalists.

“I thought the winning team gets to play home on Christmas,” Van Gundy said. Van Gundy should take note that defending champion San Antonio is also on the road Christmas Day vs. the Lakers.

Dallas natives Larry Johnson and Kurt Thomas had mixed games. LJ was an awful 1-for-10 as the Mavs chose not to double-team him on the low post as the Rockets did.

Thomas, a former Mav, scored six points on 3-of-7 shooting. He was booed by the Dallas crowd which feels he turned his back on the city by signing with the Knicks last February.

The Knicks won’t be able to sign free-agent-to-be Thomas until after the season because contract-extensions can’t be given to players on two-year contracts under the new CBA.

Thomas’ agent Jerry Hicks still wants to talk to GM Scott Layden to gauge if there’s the “necessary amount of interest,” but can’t legally begin talks. The Knicks are well over the cap.